The present invention generally relates to blood collection procedures and blood component separation methods. More particularly, it relates to new and improved methods of collecting blood into anticoagulant formulations designed to promote increased platelet yield and improved overall platelet morphology in platelet collection procedures.
Today there exists a number of automated donor hemopheresis systems for separation of blood, including whole blood into components or fractions. The systems are designed to collect one or more components, such as plasma, white cells, platelets and red cells, for further use or for disposal; to return certain components to the donor, who may be a patient; and/or to treat a component, for subsequent return to a donor. One such system is the Autopheresis-C.RTM. systems sold by Baxter Healthcare Corporation of Deerfield, Illinois, a wholly-owned subsidiary of the assignee of the present invention. That system utilizes a microprocessor-controlled instrument including automated processing programs, in conjunction with a disposable set.
The Autopheresis-C.RTM. device may, when disposable plasmapheresis set is installed therein, be used to collect plasma from whole blood drawn from a donor. A rotating membrane in a separation chamber of the disposable may in fact be wetted by an anticoagulant priming operation before blood is withdrawn from the donor, as shown in U.S. patent application Ser. No. 07/106,089, filed Oct. 7, 1987, entitled "Method for Wetting a Plasmapheresis Filter with Anticoagulant" and the corresponding PCT International Application Publication No. WO89/03229.
For the collection of platelets and plasma, the Autopheresis-C.RTM. system uses a single, two-stage set as disclosed in U.S. Pat. No. 4,851,126, entitled "Apparatus and Methods for Generating Platelet Concentrate". A set may include a rotating membrane separation chamber as set forth in U.S. patent application Ser. No. 73,378, and in corresponding Canadian Patent No. 1,261,765, as well as a centrifuge separator as set forth in U.S. Pat. Nos. 4,776,974 and 4,911,833, entitled "Closed Hemopheresis System and Method" and in International PCT Publication No.
WO88/05332 entitled "Continuous Centrifugation System and Method for Directly Deriving Intermediate Density Material From a Suspension". If an anticoagulant source is pre-attached to the set, a biologically closed system, as medically defined, can be created.
A two-stage system enables the collection of blood from a donor for separation into platelet-rich plasma and packed red cells. The red cell suspension is returned to the donor by means of the same needle used to withdraw the whole blood. The platelet-rich plasma is collected in a container. The machine and set are disconnected from the donor. The collected platelet-rich plasma is then separated into plasma and platelet concentrate, utilizing a second stage of the biologically closed set.
Another automated closed system for separating blood fractions is the CS-3000.RTM. cell separator sold by Baxter Healthcare Corporation.
During withdrawal of blood and its subsequent treatment/separation, anticoagulant must be added in order to prevent clotting of the blood within the disposable tubing and separating set during the separation or collection of the blood. The conventional method of administering anticoagulant during automated apheresis procedures is to add anticoagulant during the step of withdrawal of the whole blood from the donor's vein. Anticoagulant from an anticoagulant container is administered through tubing to a location just downstream from the phlebotomy needle at a tubing junction, where the anticoagulant tubing line merges with the nonanticoagulated whole blood tubing line adjacent the phlebotomy needle in the donor.
There are at least four separate reasons for the addition of anticoagulant to the donor's blood during extracorporeal blood procedures. The first reason is to prevent the blood from clotting as it travels through the various tubes to the blood separator of the disposable set. The second reason is to prevent the blood from clotting as it is being separated. All separators require some exposure of blood to fluid shear stresses and these shear stresses can induce coagulation or agglomeration. The third reason is to prevent the separated cells from coagulation as they are being pumped through reinfusion filters and back to the donor. The fourth reason is to provide enough nutrients and sufficient pH buffering to permit storage of the separated blood component for a required duration of time.
The demand for anticoagulant in each of the four general steps identified above depends on the particular automated apheresis procedure. Some systems may induce significantly more shear stress during blood separation than other systems and, therefore, the upper limit demand for anticoagulant would be set by the separation step. Also, the separation technology used may have different stages wherein each separation stage may have its own, different demand level for the amount of anticoagulant in the blood.
Generally, the prior art has dealt with the issue of anticoagulant demand in automated procedures by adding to the whole blood, almost immediately upon its withdrawal from the donor, enough anticoagulant to meet the highest anticoagulant demand level during the entire withdrawal, separation, return and storage procedure. The anticoagulant is added adjacent the phlebotomy needle. The anticoagulant mixes with the whole blood upon being withdrawn from the donor. The prior art systems had been directed to adding as much anticoagulant as is necessary to prevent clotting with attention being paid to an upper limit dosage of anticoagulant, beyond which a so-called "citrate reaction" may occur in the donor upon return of an anticoagulated blood component to the donor.
Human blood collected by these apheresis procedures is anticoagulated in general practice by metering in a quantity of calcium ion chelating agent such as the sodium salts of citric acid. The ratio of human blood to citrate can be adjusted and controlled by various means and in general the ratio of blood to the citrate anticoagulant is made as large as possible to prevent the donor from experiencing any signs of paresthesia.
Reducing the quantity of anticoagulant administered to the patient on collection of whole blood is desirable for the patient donor but undesirable in terms of the ultimate storage stability and quantity of special blood components collected. More particularly to date, there is still a need to improve the total number of platelet cells recovered from these apheresis procedures and to improve the cell morphology on storage to provide better blood component products.
In the past, when using citrate-containing anticoagulants such as acid-citrate-dextrose (ACD-A) and citrate-phosphate-dextrose (CPD) type anticoagulants, it has generally been believed that the ratio of whole blood to anticoagulant should be maintained in the range of 25:1 to 6:1, and the final blood pH should be maintained at about 6.8 to about 7.2. Despite these earlier efforts, it is still desired to improve upon the quantity and quality of platelet concentrates by improving platelet collection conditions and procedures.